Why is it that rigid couplings are not allowed to be used as a transition between connectors? An example would be to connecting emt to flex by using their respective connectors with a rigid coupling in between. Is it a UL listing issue and the connectors are only listed to be used with lockouts? Is conduit grounding continuity not as well maintained without the locknut? Why, then, am I allowed to thread a connector into the hub of a weather-tight box? The finish on those boxes at least appears to provide an inferior connection when compared to a rigid coupling.

There are, of course, single, complete fittings that transition directly from one conduit type to another in a much cleaner fashion. However, due to their limited production, they are much more expensive. When used throughout a project, this adds up and is hard to accept without being given a reason.

The NEC requires listing. For example, see sections 358.6 for EMT, 344.6 for RMC, 348.6 for FMC, etc., as well as 300.15 ("Fittings and connectors shall be used only with the specific wiring methods for which they are designed and listed.")

With that said, neither your complaint nor the practice is unheard of, but whether or not it's accepted is up to the AHJ.

I always thought it was pretty silly to write a 110.3 on using RMC couplers for a transition between connectors. That is especially true if there is a hard wire ground in the raceway. I have heard it argued that the quality of the connection was "not evaluated" so you couldn't count on it if the raceway was the grounding path. It still sounded pretty silly to me. The reality is, I have only seen it done a couple of times anyway.

Custom made gutters are allowed which are not listed or "evaluated". If I had our custom gutter builder weld in some couplings to use as box hubs to screw our connectors into, why would that not be acceptable? I understand that whenever an aspect of the profession isn't directly spelled out in the code book that it becomes a grey area that can be fully governed by the AHU. However, in many cases it feels like someone wanting to make their presence known (throwing their weight around) rather than using any kind of sence. Again using my example in my first post, does anybody disagree that the connection/impedance between an emt connector and a rigid coupling would prove to be better that that between an emt connector and a "Bell box" with its coating/enamel? Also, there is nothing that states directly that a coupling cannot be used as a transition and a connector actually has a shoulder to increase surface area of contact. I believe I have heard the argument that a connector has less threads of contact when compared to rigid pipe but it is still much more overall contact than a connector with a locknut. I wish the code would simply spell out this situation so that it would be held to the same standard everywhere. The only reason the "proper" connectors are so expensive is do to their low production numbers. If everyone was using them they should drop dramatically in price.

The bottom line here is if you can convince your AHJ it is OK, it is OK. Otherwise your fight is with NFPA. Convincing us isn't going to accomplish a lot. I think you should come up with code acceptable language for the right article we need to change and write a proposal for the 2023. The closer you are to the exact language you want to add, delete or change goes a long way towards therm taking it seriously along with substantiation.

I don't come here to necessary try to change the code. I usually come here to try to get my line of thinking on tract with input from like-minded individuals. There are cases like this coupling issue where some people like to create a problem where there isn't one just because they can. I was hoping somebody would comment on the situations/examples I mentioned so that I could possibly wrap my head around the ambiguity. The electrical industry has plenty of large, important, grey area issues that DO need to be ruled on by the AHU. Feeling the need to find tiny holes in the code to leap at like found treasure seems ridiculous. Thanks for all the replies. I didn't expect to get a pleasing answer but more so wanted to vent.

It is things like that that do get changes in the code made. You are making decent arguments. It is not totally out of the question that a proposal could be affected. I suppose the question is exactly what language would you change or add. That makes it easier for the CMP to decide.